The 2.4 release has basic support for PDAs – see /portal/pda in your server – the PDA portal has its own style sheet:
/portal/styles/portalstyles.css
The 2.4 release also has the workgroup portal support as well:
https://source.sakaiproject.org/svn//reference/trunk/docs/architecture/sakai_workgroup_portal.doc
Sakai 2.4 also has support for RSS, Atom, and OPML:
/portal/rss /portal/atom /portal/opml
These show sites, announcements, etc – give them a try.
After 2.4 was release a bunch of features were added to trunk in /portal
Making the PDA portal optionally eliminate iframes – experimental feature
Hierarchical site navigation
I include some properties to play with.